Numerous examples of thermal power transfer systems exist in the prior art, including relatively passive thermal power transfer loops. These systems are of particular interest in applications in outer space, where the high cost of servicing any such system and the expense of launching any such system dictates a highly reliable system with a minimal utilization of moving parts.
A heat exchange system for use in a thermoelectric power generator is disclosed in U.S. Pat. No. 3,931,532. In this system, a fluid such as potassium could be heated and vaporized for transmitting heat to junctions of the thermoelectric generator. Heat is released when the potassium condensates, and this liquid condensate is returned by a capillary flow along a wick, so that it can be reheated and vaporized to repeat the working cycle.
U.S. Pat. No. 3,897,271 discloses a static self-contained electric power generating system wherein liquid metal such as sodium can transfer heat from a nuclear heat source to generate power.
U.S. Pat. No. 4,808,240 discloses a sodium heat engine utilizing a beta-alumina solid electrolyte tube filled with liquid sodium. The sodium ions are able to pass through the tube structure, while electrons are not. The electrons are instead carried outside of the tube through an external circuit with a load for generating power. In this regard, heat is applied to the liquid sodium to elevate its pressure, and sodium ions then pass through the beta-alumina solid electrolyte to create an electrical potential difference between both sides of the electrolyte member for generating power. The gas size of the electrolyte is at a relatively low pressure to facilitate the transmission of the sodium ions across the solid electrolyte.
Conventional passive thermal power transfer loops utilizing capillary forces to sustain the operating pressure difference between the gas and the liquid phase are limited in power levels by the minimum practical pore size of their wicks. There is still a need in the prior art to increase the thermal power transfer levels that can be achieved in such systems, while maintaining the static or passive characteristics of such systems.